In internal combustion engines, it is essential that the cylinders be sealed completely airtight when the valves are closed to ensure efficient fuel consumption and transfer of power. This airtightness is achieved, among other things, by assuring that the valve heads perfectly match the valve seats. Since contact surfaces of the valves and valve seats are subject to wear and other degrading factors that effect the contact surface textures, these surfaces must be modified to re-establish the high quality seal.
It is well known among vehicle mechanics that valve seats can be machined to remove the outer surface of the seat to expose a smooth and uniform contact surface by a technique commonly referred to as "lapping". This lapping technique is accomplished by removing the cylinder head from the engine and machining the valve seats with a cutting blade. Typically, a valve seat has a profile with three different angles: a throat angle, a valve seat angle, and a top angle. Thus, a "three-angle" cutting blade or bit is used to machine a valve seat wherein each angle of the three-angle cutting blade corresponds to one of the valve seat angles to be machined. Three-angle cutting blades vary in size and shape depending on the type of cylinder head valve seat being machined. These three-angle cutting blades are currently used by all current valve seat and guide manufacturers including Berco, AZ, AMC, Vereco, Mira, Peterson, Robbi, Kwik-Way, DCM, Kansas Instruments, Sunnen, Serdi, NEWEN, T&S, Winona Van Norman, etc.
A disadvantage of the lapping technique is the risk of damage to the surface finish from vibrations, chattering, or undulations generated from flexion of the cutting bits. This problem develops because certain large-diameter cylinder head valve seat shapes require a three-angle cutting blade with a long cutting edge/surface. Cutting efforts with this long cutting edge/surface create flexions at the level of the spindle of the cutting machine or on the cylinder head, especially when dealing with valve seat material that is difficult to machine. These flexions generate vibrations, chattering, or undulations which, in turn, damage the surface finish of the valve seat making the quality of the work unacceptable by OEM (original equipment manufacturer) standards.
Another disadvantage of the lapping technique is a de-centering phenomena. As stated above, cutting efforts with a long cutting edge/surface create flexions. These flexions create an unbalanced radial cutting effort which de-centers the three-angle cutting blade.
Still another disadvantage of the lapping technique is the large number of three-angle cutting blades needed to machine different types of valve seats. Each type of engine has a different valve seat profile. Thus, one or more unique three-angle cutting blades may be needed for each type of engine.
In view of the aforementioned inadequacies of the prior art, the need exists for a cutting tool and a method to machine valve seats that substantially reduces flexions during machining and uses a universal cutting blade.